Phase Detection Autofocus Calibration Method
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Solution Overview
Problem
Current camera autofocus systems, particularly those using phase detection autofocus, face inaccuracies due to environmental changes such as temperature and humidity, leading to inefficient focus adjustments.
Innovation Solution
A calibration method that adjusts the phase linear relationship based on contrast-based autofocus procedures, determining the need for calibration through statistical distribution of focus values, and correcting the phase linear relationship using phase differences at various lens positions to improve autofocus accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the camera uses a factory default linear relationship for phase detection autofocus, then the focus operation is simple and fast, but the autofocus accuracy deteriorates due to environmental changes such as temperature, humidity, or operating voltage
Solution Approach 1:
The system performs self-calibration by automatically detecting phase differences at multiple lens positions, computing a new linear relationship, and updating the calibration parameters without requiring external intervention or manual adjustment, thereby maintaining high autofocus accuracy under varying environmental conditions
Solution Approach 2:
The system dynamically adjusts the linear relationship parameters (slope and intercept) of the phase detection autofocus based on detected phase differences at multiple lens positions, allowing the calibration parameters to adapt to environmental changes such as temperature, humidity, and operating voltage variations
2Reliability
If the camera experiments with different linear relationships for different application environments, then the autofocus accuracy is improved, but the focus time increases and efficiency decreases
Solution Approach 1:
The system performs calibration at multiple lens positions in advance to establish a comprehensive linear relationship that accounts for environmental variations, enabling rapid and accurate autofocus execution without needing to experiment with different linear relationships during actual focusing operations
Solution Approach 2:
The system uses phase difference detection feedback from multiple lens positions to compute and update the linear relationship parameters, creating a closed-loop calibration process that ensures accurate autofocus performance across different environmental conditions without requiring multiple trial executions
3Loss of time
If the camera moves the lens to the focus position in one step based on phase detection autofocus, then the focus time is reduced, but the autofocus accuracy deteriorates when the factory default linear relationship is no longer suitable
Solution Approach 1:
The system dynamically updates the linear relationship parameters of the phase detection autofocus based on real-time phase difference measurements at multiple lens positions, allowing the one-step focus mechanism to remain both fast and accurate under varying environmental conditions by adapting the calibration parameters accordingly
Data Source
AI summary
An image capture device and a calibration method of phase detection autofocus thereof are provided. A contrast-based autofocus procedure is executed to move a lens to multiple lens positions, and a statistical distribution of focus values is obtained based on the contrast-based autofocus procedure. Whether the phase linear relationship for a phase detection autofocus procedure is calibrated is determined according to the statistical distribution of the focus values. If yes, then a first phase difference detected when the lens is located at one of the lens positions is obtained, and a second phase difference detected when the lens is located at another one of the lens positions is obtained. The phase linear relationship of the phase detection autofocus procedure is calibrated according to the one of the lens positions, the first phase difference, the other one of the lens positions, and the second phase difference.